Chemicals are use used in many fields and processes to treat a variety of substances. The field of chemical treatment for use in cleaning or cleansing particularly with aqueous solutions is of increasing importance today. As regulations controlling hazardous substances become further reaching and tighter in control, there is growing pressure to carefully manage chemical usage. Further, many of the chemicals used in aqueous cleaning applications are discharged into lakes, streams, and rivers and can contaminate our groundwater and environment.
A market has emerged over the last couple of decades to automatically wash automotive vehicles as more and more people do not have access to washing facilities nor time or desire to clean their own cars. The popularity of drive through car washes today has become a large business for chemical companies as a conduit to sell and consume various cleaning and treatment chemicals. Further, there is considerable competitive pressure to clean cars adequately for the best value so as to gain repeat business. This activity is driving unknown and excessive chemical usage and its subsequent damage to the environment. The typical car wash has little or no knowledge of the amount of chemical used for each washing event. The current methods of dispensing have inconsistencies and create excess waste.
Many of the car wash systems are using old technologies such as dosing pumps and inaccurate eductors to draw concentrated chemicals and mix them with a supply of washing water. The dilution ratios can vary substantially and change without notice. Further, even the best systems often do not supply a constant dilution rate during their dispensing. Managers and operators of the car wash need to understand the cost or chemical target per car in real time for each of the chemicals being used. The typical information that managers or operators get today is a visual indication of bulk usage only after perhaps dozens or hundreds of wash events. Further, making changes to the dilution rates are often cumbersome and inaccurate, particularly since there is no convenient and immediate method to measure their use in real time. Often, adjustments of the dosing or eduction are coarse and can be at cross purposes. The supplier of the chemicals desire that they use and sell more chemicals, while owners want to reduce their chemical usage and operating expense. Often, it is not known how the system is performing or who has made any adjustments to it.
Considerable technical progress has been made in the field of dispensing chemicals particularly as it relates to industrial washing systems such as car washes. These systems are gaining in complexity and sophistication but are still lacking necessary controls to keep them from operating as open-loop processes. It is a challenging pursuit to get fluid handling devices to operate long-term with the very caustic, acidic, and oxidizing chemicals used in cleaning. Often these chemicals range from less than 1 pH to 14 pH.
Typical Car Wash
A typical car wash chemical dispensing system can be seen in FIG. 2. A bulk container of concentrated chemical, which is typically sold in a tight-head 5-gallon polyethylene container, is connected to a venturi style eductor such as those used in a Hydrominder™, which is manufactured by Hydro Systems Company. This venturi eductor is used to create a crude dilution of the concentrated chemical in a batch tank as the process water flows through the eductor. The operator fills the batch tank manually or it is filled automatically using a float to sense the tank level. The batch tank holds a diluted aqueous solution of chemical and process water. A dosing-type positive displacement injector pump is pneumatically driven to dispense the diluted solution directly onto the cars usually controlled by PLC driven solenoid valves. The rate of batch chemical pulses is controlled by pneumatic flow controls which regulate the supply of air driving the pump. FIG. 3 shows the characteristic chemical concentrations that result at the dispensing nozzle. The final concentration varies according to time and is dependent on the relative concentration of the batching process, the dosing pump rate, and the flow rate and pressure of the incoming process water. There are many process variables which create difficulty in fine-tuning the dilution rate; incoming water pressure and flow rate, eductor setting, and dosing pump rate and displacement and batch chemical concentrations. These systems need to be simplified and the variables reduced to effectively determine the amount of chemical being used in real time and to subsequently control their usage.
Improved Car Wash
With the development of Chem-Flex™ Injectors (venturi eductors) manufactured by Hydra-flex Incorporated, it is now practical to provide consistent long-term dilution rates ranging from 3:1 to 2000:1. With these devices, stable chemical dilution rates are achievable when directly feed with concentrated chemicals and without an intermediate batching process. A system which is stable in operation can be used to achieve a repeatable process. Even though a venturi-based chemical dispensing system using Chem-Flex™ type injectors is considerably more compact and simpler in operation; there is still no convenient method to determine how much chemical is being fed into any injector in real time. The method of dispensing chemicals remains open-loop without chemical feed rate control. It is only after several chemical dispensing events that the level of the chemical container can be seen to change. Considering that certain cleaning chemicals can have a dilution rate of 400:1, it would take over three gallons of dispensed diluted chemical solution to be able to resolve a single ounce of concentrated chemical. Considering that the level of a 5 gallon container has approximately 12 inches of chemical head and holds 640 ounces of chemical, just one ounce of chemical changes the level by 0.019″ which is nearly impossible to read visually. Using this improved eductor based system, it is still not possible to obtain a per wash cost in real time and requires many wash events averaged over a significant time before meaningful information can be obtained to make process corrections.
What is needed is a dosing system that is both accurate and precise without flow pulsations and able to blend concentrated chemicals into a high-pressure stream for spray dispensing.